A constant complaint of loading dock workers, mechanics and general bystanders is the odor and smoke which is emitted from diesel engines during cold start up and prolonged idle in cold weather at places such as truck stops, freight terminals and loading docks. The exhaust gas which is emitted under these conditions is known as white smoke because of its light gray to white color. White smoke consists of unburned fuel in the form of small droplets which condense as they reach their saturation temperature. This condition will persist until the engine is run under load and warmed up.
In addition to the odor associated with white smoke, by allowing unburned fuel and consequently unburned hydrocarbons to be emitted into the atmosphere, engines operating in many areas will not be able to meet the rigorous National Air Quality Standards for Hydrocarbons and ozone levels which are to be fully implemented by 1994. Consequently, it can be seen that there is a pressing need for an inexpensive and reliable system for eliminating white smoke emissions from diesel engines during cold starts and prolonged idle in cold weather.
In an attempt to reduce white smoke emissions from diesel engines it has been proposed to significantly increase the temperature of the intake air into the engine's cylinders in order to more completely ignite the diesel fuel injected therein. However, this in-cylinder combustion technique requires the incorporation of a burner or other type of heater into the air intake system as well as sensors and an independent control system to monitor and operate the heater. As can be appreciated, such a system will be expensive to employ, and would require extensive modifications to the engine's air intake system. Further, while raising the air intake temperature improves in-cylinder combustion, a portion of the injected fuel remains unburned. Consequently, at low ambient air temperatures, this unburned fuel will condense resulting in white smoke when emitted from the engine.
While not related to the above mentioned problem, it has been known in the art to increase the temperature of diesel exhaust gas and particulate filters positioned within the exhaust gas stream by way diesel fuel burners or electric heating elements. Examples of such are disclosed in U.S. Pat. No. 4,383,411 issued to Riddel and U.S. Pat. No. 4,544,388 issued to Rao et al. respectively. As can be seen from the above disclosures, it is only after the engine has been operating for an extended period of time that the burner or heating elements are activated, and this activation is initiated for the purpose of regenerating the "full" ceramic particulate trap. Likewise, upon completion of the regeneration cycle, the burner or heating elements are deactivated until such time as the ceramic particulate trap once again requires regeneration. As mentioned above, it is during start up and prolonged idle at low ambient air temperatures that unburned fuel (unburned hydrocarbons) condenses and results in the undesirable white smoke. Therefore, the above mentioned systems do not aid in lessening the irritating odor and smoke associated with white smoke.
As can be seen from the foregoing, an inexpensive and reliable system for eliminating white smoke emissions from diesel engines during cold starts and prolonged idle in cold weather is needed both for reducing hydrocarbon emissions and for eliminating much of the odor associated with white smoke. Such a system would broaden the overall acceptance of diesel powered vehicles.